1. Field of the Invention
The present invention relates to the synthesis of acyl cyanides and, more especially, to the synthesis of acyl cyanides by reacting acid halides with an alkali metal cyanide in an anhydrous reaction medium.
2. Description of the Prior Art
The acyl cyanides are known intermediates for a variety of organic syntheses, for example the production of herbicides.
FR 2,353,524 describes a synthesis of benzoyl cyanide C.sub.6 H.sub.5 COCN by reacting benzoyl chloride with a molar excess of sodium cyanide in the presence of a nitrile of a carboxylic acid and copper cyanide.
FR 2,346,323 describes a similar, but much more general reaction, since it is applicable to an entire class of acyl cyanides, and entails reacting sodium cyanide with an excess of acid halide in the presence of copper or zinc cyanide.
The above processes present the disadvantage of requiring the presence of heavy metals and therefore mandate complicated treatments to avoid their presence in the reaction effluents.
Tetrahedron Letters (Pergamon Press) No. 26, pages 2275-2278 (1974) describes a process limited to the synthesis of benzoyl cyanide by reacting sodium cyanide with benzoyl chloride in solution in methylene chloride and in the presence of tetrabutylammonium bromide; the C.sub.6 H.sub.5 COCN yield based on C.sub.6 H.sub.5 COC.sub.1 converted does not exceed 60%.
FR 2,364,894 describes the synthesis of C.sub.6 H.sub.5 COCN by reacting C.sub.6 H.sub.5 COC.sub.1 with NaCN in a solvent in the presence of benzoic anhydride (C.sub.6 H.sub.5 CO-O-CO-C.sub.6 H.sub.5) or of products which can generate benzoic anhydride under the reaction conditions.
The preferred amount of benzoic anhydride ranges from 0.03 to 0.1 mole per mole of benzoyl chloride. This presence of benzoic anhydride complicates the recovery of the benzoyl cyanide.